Time-gated perturbation Monte Carlo for whole body functional imaging in small animals

Abstract

This paper explores a time-resolved functional imaging method based on Monte Carlo model for whole-body functional imaging of small animals. To improve the spatial resolution and quantitative accuracy of the functional map, a Bayesian hierarchical method with a high resolution spatial prior is applied to guide the optical reconstructions. Simulated data using the proposed approach are employed on an anatomically accurate mouse model where the optical properties range and volume limitations of the diffusion equation model exist. We investigate the performances of using time-gated data type and spatial priors to quantitatively image the functional parameters of multiple organs. Accurate reconstructions of the two main functional parameters of the blood volume and the relative oxygenation are demonstrated by using our method. Moreover, nonlinear optode settings guided by anatomical prior is proved to be critical to imaging small organs such as the heart.

Fig. 1

(a) The original high resolution mouse model (b) The resized mouse model with five organs (heart {teal}, stomach {green}, liver {yellow}, kidneys {red} and lungs {purple} extracted from Fig. 1(a))

Fig. 2

(a) Time cost with increasing number of nodes, from 10⁵ to 10¹⁰ with homogeneous optical properties. (b) Computational time when simulating different gates and detectors.

Fig. 3

Typical Jacobians for three different time gates in a mouse model. First column: TPSF simulated and selected time gates (first half maximum, maximum and last half maximum of TPSFs). Second column: Sagittal plane of the synthetic phantom and normalized Jacobians corresponding to each selected time gate. Third column: Transverse plane of the murine model with associated normalized Jacobian. The Jacobians are plotted in log scale to provide better visualization.

Fig. 4

Anatomically guided nonlinear sampling: (a) Evenly spanned source (black dots) and detectors (red dots) configuration and reconstructed (c) blood volume and (d) oxygen saturation; (b) dense source and detector pairs around the overlapping organs and the reconstructed (e) blood volume and (f) oxygen saturation. The heart and stomach have been delineated with white lines.